1. Field of the Invention
The present invention relates to a device for automatically locking the release of an electric shutter in case the power supply voltage becomes lower than a limit level.
2. Description of the Prior Art
In an electric shutter, a time output signal indicating the time from the opening of the shutter aperture is compared with a shutter speed output signal indicating an appropriate exposure time calculated from the luminance of the object, lens aperture and film sensitivity, and a solenoid for blocking the shutter closing movement is deactivated to close said shutter aperture when a determined relationship is reached between said two output signals, but such exposure time control function cannot be conducted properly if the power supply voltage becomes lower than a determined limit level. For this reason there is already known a shutter release locking device which prohibits the opening function of the shutter aperture in case the power supply voltage becomes lower than the determined limit level. Such shutter release locking device is provided with a voltage detecting circuit adapted for detecting the power supply voltage and deactivating the solenoid for blocking a shutter aperture closing member prior to the opening movement of shutter aperture in case thus detected power supply voltage is lower than the determined limit level, and blocking means for blocking a shutter aperture opening member in response to said solenoid deactivation prior to the shutter aperture opening function. However, in case the luminance of the object is so high that the appropriate exposure time is far shorter than the minimum exposure time achievable with the electric shutter, the aforementioned determined relationship is reached between the shutter speed output signal for said appropriate exposure time and the time output signal even before the opening function of the shutter aperture, so that said solenoid is deactivated before the shutter aperture can be opened independently from said voltage detecting circuit, thereby activating the blocking means to disable the shutter release. Such shutter release locking under certain exposure condition despite of a sufficiently high power supply voltage is undesirable because such situation may be mistaken by the camera operator as a lowered power supply voltage.